660 EEPORT— 1888. 



nearest Upper Devonian vocks and Culm Measui-es. From the strike of the Upper 

 Devonian rocks he considered that they wcnild be found under the Trias of the 

 Vale of Taunton, and miprht trend northward under the Brid^ewater Levels, till 

 cut otf by fault or unconformity bringing on the Carboniferous beds of normal type. 



He believed a very careful comparison of the relations of the Belgian Lower 

 Carboniferous and Upper Devonian rocks with the Culm Measures and Upper 

 Devonian rocks of Devon and Somerset would throw much light on the question. 



Lastly, brief allusion was made to the absence of the Lynton beds east of Luccot 

 Hill, and to the possibility of their occurrence, as also of the presence of Foreland 

 grits in the north of the Quantocks. 



SATURDAY, SEPTEMBER 8. 

 The following Papers and Report were read : — 



1. Comparison of the principal Forms of Dlnosauria of Europe and America. 



By Professor 6. C. Marsh. 



2. 17(6 Evolution of the Mammalian Molar Teeth to and from the Trituher- 

 cular Type} By Henry Fairfield Osborx. 



Out of 82 species of mammals from the lowest Eocene of America (Puerco), 

 all but four have tritubercular superior molars. From this type it is demonstrated 

 that the molars of many of the Marsupialia of the Carnivora, Insectivora, Lemu- 

 roidea and Primates, Ungulata, &c., are derived, by the addition of cusps. To this 

 type it is demonstrated that the molars of the Triassic and Jurassic mammalia lead. 

 It is a central type. 



The histor\-"of each of the cusps can be traced in all the mammals in which the 

 molars have passed through the tritubercular stage. A nomenclature is therefore 

 proposed as follows: the protocone, for the cusp which represents the primitive 

 reptilian cone ; the para and metacones, for the cusps on either side of this. These 

 rotate inwards in the lower jaw and outwards in the upper jaw, to form the 

 tritubercular type. In the lower molars a heel is next formed, the h/poconid, this 

 leads to the formation of the intermediate cusps upon the upper molars, the />ara 

 and metaconnles. Finally the heel is formed upon the upper molars, the hypocone, 

 completing the sexitubercular crown. 



These stages of evolution are also named as follows : protodont, primitive 

 reptilian cro^vn stage ; triconodont stage, with the large central and two lateral 

 cones; tritubercular (Cope); sp.rituberrular, the parent ungulate type with six 

 tubercles, and the qundrituhemilar. The lower molars pass more rapidly through 

 the tritubercular to the tuhercular-sectorial (Cope) and quadrituhercular stages. 



The development of the cusps is believed to be, in a measure, mechanical 

 (Lamarck, Pivder, Cope) : a. New cusps appear at points of vertical interference 

 between upper and lower molars; b. Cusps take new shapes as a result of hori- 

 zontal interference between upper and lower molars. 



Not all mammalia are believed to have acquired this type. Those which have 

 not are believed to have become extinct, this type having favoured the lines which 

 acquired it. At any one period we find j)ro(jre.'<dve, conservative, central and pifr- 

 sistent types of molars, standing at various stages of the tritubercular evolution. 



3. Oil the Gigantic Size of some Extinct Tertiary Mammalia. 

 By Professor A. Gaudrt. 



The author drew attention to the veiy large size attained by some of the 

 mammalia in later geological times, and instanced especially the skeleton of Elejihas 



' Published in exfenso in the American Katvralist, December 1888. 



